Rom 14:5 One person regards one day above another, another regards every day {alike.} Each person must be fully convinced in his own mind.

The tricky part here is that the only basis we have for being convinced is the word itself. And if the Bible addresses an issue, it's no longer something that different people can take differing positions on. I think Paul is saying that we really can have no basis for insisting on one position over another. If the word addresses the matter, it is set, and if not.. what other source do you have to stand on?

Colossians 2:16 NASB -

Therefore no one is to act as your judge in regard to food or drink or in respect to a festival or a new moon or a Sabbath day

5/21/2009
9/30/2009 reworked some
5/18/2014 added col 2:16